1. Field of Invention
This invention relates to the removal of dust, lint and also static charge, simultaneously, from film. This is extremely important when making prints from photographic negatives. It is necessary to remove all dust and lint from the negatives so that a clean print can be made that is unblemished by the imaging of dust and lint adhering to the film. Static charge on film attracts dust and lint which is then bound to the film by the electrostatic attraction. Therefore, it is necessary to remove the static charge from the film in order to release the dust and lint and also to prevent it from being attracted back to the film after it is removed.
2. Description of Prior Art
Many methods have been devised to eliminate static charges from plastic film. The most common method is by making the surrounding air electrically charged or ionized both positively and negatively, thus allowing the charges on the film to be neutralized by contact with oppositely charged molecules of the adjacent air. However, other methods which remove the charge by conduction are used also. These include such methods as running conductive materials such as metallic or conductive brushes, wipers or conductive liquids over the surface, or by increasing the conductivity of the surrounding air such as by raising the humidity of the air.
Static charge on non-conductive plastic surfaces usually develops as the result of contact with another plastic item. Such plastic surfaces, or items in contact, have an atomic valence attractive force that holds them together. This force is electric in nature and is of the variety that holds materials together. Separation of these items results in a rending of some of the negatively charged electrons from one of the surfaces by the stronger attractive force of the other one, and the adherence of those electrons to that surface. Thus, the surface that has lost electrons is left with an electric charge to again attract negatively charged electrons, and has thereby acquired a positive charge. And, the surface which has gained a surplus of electron has thereby acquired a negative charge.
This is a classic example of how static charges develop. However, static charges are known to develop in many ways and on many surfaces and bodies that do not fit the above example. Static charges are transferrable through conductive means such as in a Van de Graff generator, or by accumulation of charge on an electrically isolated body through friction means, such as an aircraft or car by friction with the passing air. Charges can also be accumulated from direct contact with high voltage sources or by transmission from a surrounding ionized atmosphere.
Except in a vacuum, static charges tend to dissipate or leak off through the conductivity of the surrounding atmosphere. The greater the conductivity of the atmosphere the faster the charge will leak off. In humid weather, the moisture in the air makes the air more conductive than in dry weather when there is little moisture in the air. Thus, we seldom encounter static charge on a humid day and frequently encounter it on a dry day.
Static charges are transferrable. Static charge acquired by our clothing is transferred to our body or parts of our body. And, when we approach an object of different electrical potential (usually a ground potential), we experience an electrical discharge as electrons arc from our finger to that object, or vice versa. Static charge can also be transferred from our bodies to tools or other items we contact. These tools, in turn, can impart the charge to a voltage sensitive component causing damage.
Although an in-depth discussion of the principles of the many techniques for removing static charge a well as eliminating dust, lint and other particulate matter can be pursued, let us limit the range of this discussion to the immediate scope as defined by the application of the devices that will emanate from the subject invention.
This invention is concerned with devices for the removal of static charge, dust and lint by the use of a device that incorporates the blowing of ionized air over plastic film surfaces, and the control and augmentation of such devices. In such devices, air that is ionized both positively and negatively, so as to neutralize both positive and negative charges on the surfaces, is imparted with a sufficiently high velocity to convect the dust and lint off and away from these surfaces. The device also is configured to impinge on both surfaces of a typical plastic film, Thus, it incorporates structures to direct the air simultaneously to the opposing surfaces. The configuration embodies two parallel structures, usually referred to as jaws, between which the film is passed. The device is normally inactive until the film is inserted between the jaws. At that time a mechanism means automatically activates the device.
Devices of this design have been in existence for several years. They are referred to an anti-static film cleaners. U.S. Pat. No. 4,194,232 James M. Cumming et al. and U.S. Pat. Nos. 4,750,080 and 4,805,068 Newell E. Cumming et al. describe two such devices, as does my earlier U.S. Pat. No. 4,635,161 which was later expanded by my U.S. Pat. No. 4,768,126. Although there are significant differences between Cummings devices and my own, they do have basically the same configuration, that of having two jaws between which the film is placed.
U.S. Pat. No. 4,194,232 incorporates compressed air escaping at high velocity through small holes directed toward the film from above and below and, although there is no claim for an activation means, the text describes the interruption of a light beam that transects the film path through the device. Interruption of this light beam by the presence of the film turns the system on.
U.S. Pat. No. 4,750,080 also incorporates compressed air, similar to that above, and claims four light beams (i.e. electro-magnetic beams), two on each side, the interruption of which initiates activation of the device.
U.S. Pat. No. 4,805,068 uses brushes instead of high velocity air which contact the film both top and bottom to remove the dust, while the device is activated by the interruption of light beams. However, there is no claim for the use of a light beam.
U.S. Pat. No. 4,635,161, which is my patent, is primarily a device for eliminating static charge, dust and lint from surfaces, including plastic film surfaces, and the configuration as a film cleaner is described in the text. However, being a basic patent for the invention of a device that uses constant DC high voltage for the elimination of static charge, no specific claims were made for a specific application. However, in practice some film cleaners manufactured under this patent do incorporate the interruption of a light beam to activate the device.
Although the initial devices manufactured under U.S. Pat. No. 4,635,161 incorporated the use of compressed air which was converted to a high velocity as it passed through small apertures, later models used the high speed impeller design claimed in my U.S. Pat. No. 4,768,126 to produce high velocity air for the removal of dust and lint as well as the static charge. Some of these devices also utilized the interruption of a light beam to activate the system.
There is another characteristic of all of the above discussed film cleaners that use high velocity air as a means of removing the dust and lint. That is the "Bernoulli Effect". When air flows from an opening and impinges on a flat surface spaced near and perpendicular to the opening, the air flow changes direction to follow the contour of the flat surface. As the air flows away from the opening, the pressure of the flowing air decreases, resulting in a lower air pressure in the region of the opening than that of the surrounding atmosphere. If the flat surface is a thin plastic film, such as that used in photography, the effect will be that the film will be acted upon by the greater atmospheric pressure and forced against the opening from which the air is flowing.
This is undesireable for photographic film, as the film can be scratched if there is any roughness to the surfaces near the air flow opening. To combat this effect, film cleaners using high velocity air used polished smooth surfaces in the area near the air openings to prevent scratching. However, this technique is not always satisfactory and scratches on film can occur as rough spots develop with use or foreign particulate matter accumulates.